In the drilling and servicing of oil and gas wells, it is known to employ various types of pipes. Such pipes include drill pipe, drill collars, production tubing, well casing/liners and riser pipe. While not strictly considered pipe, some solid elongate members such as sucker rod are also handled and will be considered as pipe herein.
The pipes are manipulated by a well rig to either drill a well or service an already drilled well. The well rigs are sometimes called drilling rigs or servicing rigs but will be called generally a well rig or a rig herein.
Such pipes are delivered to the rig, and laid in individual joints horizontally upon a pipe rack. In the case of land wells, the pipe is typically delivered by a flat-bed truck. For offshore wellsite operations, the pipe is delivered by barge or on a large floating vessel.
In order to use the pipe on the rig, it is necessary to pick up the pipe, which is to transport the pipe from the pipe rack to the rig floor and then manipulate it into alignment with well center such that it can be moved into the well. When the rig is operating to remove pipe from the well, the rig operates to “lay down” the pipe. Sometimes pipe is maintained on the rig floor standing up. If this occurs, the pipes are still manipulated into or out of alignment with well center.
Manipulating pipes up and down relative to the rig and into or out of alignment with well center presents certain hazards to personnel on the rig floor. The rig floor can vary considerably in height.
These concerns are further complicated by the use of slant rigs, where the pipe must be presented in alignment with a well center that is not vertical. While a vertical rig can rely on gravity to move a pipe into alignment with well center, this is not true in a slant rig.
In addition, the actual slant angle at which a slant rig works can vary.